Defrosting system with food compartment shunt switch



L. J. MANN E AL DEFROSTING SYSTEM WITH FOOD COMPARTMENT SHUNT SWITCH Filed July 19, 1965 "EL I179 MEI? "'29 M INVENTORS L eonara' J. Mann T heir Af/omey United States Patent C) DEFROSTING SYSTEM WITH FOOD COMPART- MENT SHUNT SWITCH Leonard J. Mann, Dayton, and Robert S. Hanson, Kettering, Ohio, assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed July 19, 1965, Ser. No. 472,801 5 Claims. (Cl. 62-156) This invention pertains to refrigerating apparatus and more particularly to means for defrosting an evaporator of a frost free refrigerator when it becomes coated with an objectionable amount of frost.

Although many devices have been devised for defrosting an evaporator when there is a predetermined buildup of frost thereon, none of such devices has achieved any widespread commercial success. Instead, whether needed or not, it has been customary to defrost the evaporator at timed intervals even though this is wasteful and unnecessarily raises the temperature of the compartments for an undesirable amount during such defrost periods.

It is an object of this invention to provide a simple economical inexpensive system which will initiate a defrosting period only when the evaporator becomes coated with an objectionable amount of frost.

It is another object of this invention to provide a simple arrangement for continuing the operation of the refrigerating system when the evaporator becomes coated with an objectionable amount of frost to accelerate the initiation of a defrost cycle.

These and other objects are attained in the form of refrigerator illustrated -in the drawings in which frost does not collect in the freezing compartment. In this refrigerator air is drawn separately from above and below freezing compartments into a mixing chamber between the compartments in which a finned evaporator is located. The air is drawn between the fins of the evaporator and discharged by a fan back into the compartments in a proper portion to maintain the freezing compartment at low freezing temperatures and to maintain the above freezing compartment at satisfactory above freezing refrigerating temperatures. Since the evaporator is normally maintained below water freezing temperatures, it gradually collects frost from the circulating air. This coating of frost gradually reduces the amount of heat transferred from the air to the evaporator. The temperature of the below freezing compartment is more readily maintained at satisfactory refrigerating temperatures than the above freezing compartment.

To provide satisfactory control of the temperatures in both compartments as well as to initiate defrosting of the evaporator when an objectionable amount of frost collects thereon, we provide normal cycling controls responsive to the temperature of the below freezing compartment and a second control responsive to the temperature of the above freezing compartment for keeping the compressor in operation as long as is required to maintain the desired temperature in each of these compartments. When the evaporator becomes coated with frost as the compressor continues to run, its temperature will be lowered until the compressor can no longer lower the temperature. In accordance with our invention we provide a defrost control which initiates the defrosting of the evaporator when a temperature slightly above the minimum temperature of the evaporator is reached during prolonged operation of the compressor. This defrost control is accomplished through the .use of a double throw bimetal switch mounted on the portion of the evaporator which is contacted first by the air circulating from the above freezing compartment where the frost customarily collects first and in greater amount. This defrost control switch is connected in series with the control switches 3,316,729 Patented May 2, 1967 responsive to the above and below freezing compartment temperatures which are connected in parallel with each other but in series with the motor compressor unit. When frost accumulates on the evaporator, the below freezing continues to receive adequate cooling, but the above freezing compartment warms up, closing the second control to continue operation of the system to lower below normal the temperature of the evaporator. When the evaporator reaches a sufficiently low temperature, the defrost limiter switch is actuated to energize the defrost heater circuit and to deenergize the motor compressor unit. This continues until the temperature of the evaporator is sufiiciently high to melt the frost therefrom and to reset the defrost control switch to the normal position.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein preferred embodiments'of the present invention are clearly shown.

In the drawings:

FIGURE 1 is a fragmentary vertical sectional view through a two-compartment frost-free forced air refrigerator embodying one form of my invention;

FIGURE 2 is a wiring diagram for the refrigerator illustrated in FIGURE 1 also disclosing my invention; and

FIGURE 3 is a fragmentary vertical sectional view showing the entrance passage from the above freezing compartmentto the mixing compartment showing the location of the defrost control switch.

Referring now to the drawing there is shown an insulated refrigerator cabinet 20 provided with an insulated rear wall 22, insulated side walls 24, an insulated top wall 36 and insulated upper and lower front doors 26 and 28 enclosing .an upper below freezing food storage compartment 30 and a lower above freezing food storage compartment 22. The bottom insulated wall is not shown but may be conventional. Between the compartments 30 and 32 there is provided an insulated horizontal partition wall 34.

The below freezing compartment 30 is provided with a false bottom wall 40 of sheet metal which rests upon the top of the vertical fins 41 of a refrigerant evaporator 42 located within a mixing compartment 44 which is located between the false bottom wall 40 and the partition wall 34. The top of the above freezing compartment 32 is provided with a metal wall 54 having an air entrance 62 to the passage 56 which connects with a passage 64 extending through the partition wall 34 to the rear corners of the evaporator 42. The air from the passage 64 flows forwardly on both sides of the mixing chamber 44 in heat transfer relation with the side portions of the evaporator 42 to the front thereof as is more extensively illustrated in Patent No. 3,105,364, .issued Oct. 1, 1963.

Beneath the front edge of the false bottom wall 40 there is provided an air entrance 84 to the mixing compartment 44 where the air from both compartments mixes as it passes the accumulator prior to passing through the central portion of the evaporator 42. The rear of the false bottom wall 40 is porvided with an opening 86- over which is located the shroud 88 through which is drawn the air from the rear central portion of the evaporator 42. This air is drawn into the center of the centrifugal fan 90 which is driven by an electric motor 92 located Within a recess 94 in the rear wall. The fan 90 has an upward discharge shroud 96 for delivering the greater portion of the cold air to the below freezing compartment 30. A small portion of the air is discharged through a downwardly extending discharge shroud 121 and passages 123 and 125 to an air valve 127 which controls the discharge of the air through the outlet 143 into the above freezing compartment 32. The air valve 127 has a valve element 137 operated through a valve stem by a fluid motor 129 which includes a metal bellows en- 161 connected by a capillary tube 163 to a thermostat bulb 166 mounted in heat transfer with the top wall of the below freezing compartment 30 above the discharge shroud 96. This switch 159 is preferably set to open when the compartment 30 reaches a temperature of 2 F. and to reclose when the compartment 30 reaches a temperature of +l1 F. With this type of control, as long as the evaporator 42 is comparatively free of frost, both compartments will be maintained at desirable refrigerating temperatures. The valve 127 is preferably set to close at about 34 F. and to open fully at about 39 F. However, if desired this valve may be replaced by a manually adjustable valve.

According to my invention we provide a switch which closes under such circumstances of high temperature in the compartment 32 to continue operation of the motor compressor unit after the compartment 30 is sufficiently cooled. This provides increased cooling for both compartments 32 and 30 and reduces the temperature of the evaporator 42 to speed the initiation of a defrost cycle.

In FIGURE 1 this takes the form of a switch 179 operated to closed position by an operating member 181 when the valve 127 passes beyond its wide open position at about 39 F. As shown in FIGURE 2, this switch '179 is connected in shunt or parallel circuit relation with the cycling control. switch 159 by having their electrical connections connected to the junctions 220 and 222. When the switch 179.closes because of the coating of frost .thereon, the temperature of the evaporator 42 will continue to fall.

We take advantage of this fall in temperature by providing a double throw bimetal snap acting temperature re- 'sponsive switch 175 which is mounted upon the rear portion of the evaporator 42 in the rear entrance 'passage from the above freezing compartment 32. As the frost accumulates on the evaporator 42, it also accumulates upon the defrost control switch 175 and insulates .it from the air flowing from the above freezing compartment 32 in the same manner that the evaporator 42 is insulated by the frost. Therefore, the defrost control .switch 175 becomes more and more responsive to the internal temperature of the evaporator 42. As shown in FIGURE 2, this defrost switch 175 includes a movable bimetal operated contact member 224 and normally stationary contacts 226 and 228. The switch 175 normally has the movable contact 224 in the left position shown in FIGURE 2. It is preferably provided with a snap action arrangement which may be of any form desired such as is provided by the toggle spring 230.

The compressor motor 147 is connected between the supply conductor 155 and the junction 222. This connects it in series with the cycling control switch and the above freezing compartment switch 179 which are in parallel with each other and with the normally closed contacts 224-and 226 of the switch 175. The fan motor 92 is connected in parallel with the compressor motor .147. The compressor motor 147 drives the pump 145 which pumps compressed refrigerant to the condenser .151 from which liquid refrigerant flows through a restrictor 152 to the evaporator 42 where the liquid re-.

frigerant evaporates and in this state, passes through the accumulator 80 and the suction conduit back to the pump 145. The switch 175 is set to open the contacts 224 and 226 when its temperature reaches a 18 F.

Under conditions of accumulating frost upon the evaporator 42 and the Outside casing of the switch 175, the

compressor motor 147 will be cycled by the cycling control switch "159 to maintain the below freezing compartment 30 at desired temperature levels at all times. The above freezing compartment 32 will be supplied with cold air in an amount adjusted by the valve 127 to keep its temperature from falling below about 34 F. As the evaporator 42 becomes more and more frosted, the valve 127 will open wider since the air delivered to it will be warmer because of the reduced cooling of the air by the frost coated evaporator 42. That is, the frost coating will act as an insulator to reduce the heat transfer between the refrigerant in the evaporator 42 and the air flow through the mixing chamber 44 around the evaporator 42. As this condition grows, the below freezing compartment 30 will continue to be maintained between proper temperature limits since the switch 159 will cause operation of the compressor motor 147 to continue until the temperature of 2 F. is reached.

The air delivered to the compartment 30, however, will be somewhat less cold due to the insulating effect of the frost upon the evaporator 42. The delivery of the warmer air through the valve 127 to the above freezing compartment 32 will require the valve 127 to open wider, with the accompanying inherent rise in temperature in the compartment-32 because of the normal characteristics of the valve 127. When the valve 127 goes beyond its fully open position and no increased amount of air can pass through it, the switch 179 will be closed at a temperature of about 39 F. Under such circumstances the switch 1'79 will be closed continuously causing continuous operation of the compressor motor 147 in order enough to reach the tripping point 18 F. of the defrost control switch 175. When this is reached, the contacts 224 and 226 will separate to deenergize the compressor 'motor 147 and the fan motor 92. This will stop the operation of the compressor motor and the refrigerating system thereby allowing the frost to melt from the evaporator 42.

To speed the defrosting operation, the switch has the alternate stationary contact 228 which is engaged in the open circuit position of the contacts 224 and 226 by the movable contact 224. This will energize the defrost heater 177 which is connected to the contact 228 and also connected through a bimetal safety switch 178 with the supply conductor 155. Current is then supplied through the supply conductor 169, the moveable contacts 224 and 228 through the heater 177, and the switch 178 to the supply conductor 155. This rapidly heats the evaporator 42 and causes the frost to melt from it. After the meltingof the frost is completed, the evaporator 42 will further rise in temperature until the predetermined resetting temperature, possibly 55 F. is reached. This is the reset tripping point of the switch 175 which will then return to its normal position shown in FIGURE 2 to restart the refrigeration system through the closed switches 159 and 179 to resume operation of the compressor motor 147.

While we have illustrated defrosting through the stopping of the compressor and through the use of an electric heater, other forms of defrosting means may be substituted if desired. This system provides a simple practical defrost system which is substantially free of complications and which defrosts the evaporator 42 only when required to conserve energy and to maintain the best possible refrigerating conditions.

While the embodiments of the present invention as herein disclosed, constitute a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. A refrigerator including means enclosing a below freezing storage compartment and an above freezing storage compartment, means forming a mixing compartment separated from said compartments, an evaporator portion associated with said mixing compartment, means for circulating air from said below and above freezing compartments through said mixing compartment and returning the cooled air to said below and above freezing compartments in amounts sufficient to maintain normally said compartments at desired below and above freezing temperatures, refrigerant liquefying means operatively connected to said evaporator portion, a defrosting switch having a set of normally closed contacts, electrical operating means for said liquefying means, a thermostatic cycling control switch responsive to temperatures of said below freezing compartment and a second temperature responsive switch responsive to the temperature of said above freezing compartment, said cycling control switch and said second switch being connected in parallel electric circuit with each other and in series circuit with said normally closed contacts of said defrosting switch and said electrical operating means for controlling the temperature of said evaporating portion to hold desirable refrigerating temperatures in said compartments, means for electrically energizing said circuits, said defrost switch also having operating means responsive to a predetermined low temperature of said evaporator portion for operating to open position said normally closed contacts to deenergize said electrical operating means.

2. A refrigerator including means enclosing 2. below freezing storage compartment and an above freezing storage compartment, means forming a mixing compartment separated from said compartments, an evaporator portion associated with said mixing compartments, means for circulating air from said below and above freezing compartments through said mixing compartment and returning the cooled air to said below and above freezing compartments in amounts sufiicient to maintain normally said compartments at desired below and above freezing temperatures, refrigerant liquefying means operatively connected to said evaporator portion, a defrosting switch having a set of normally closed contacts, means for defrosting said evaporator portion, electrical operating means for said liquefying means, a thermostatic cycling control switch responsive to temperatures of said below freezing compartment and a second temperature responsive switch responsive to the temperature of said above freezing compartment, said cycling switch and said second switch being connected in parallel electric circuit with each other and in series circuit with said normally closed contacts of said defrosting switch and said electrical operating means for controlling the temperature of said evaporating portion to hold desirable refrigerating temperatures in said compartments, means for electrically energizing said circuits, said defrost switch also having operating means responsive to a predetermined low temperature of said evaporator portion for operating to open position said normally closed contacts, and means responsive to the opening of said normally closed contacts for rendering effective said defrosting means.

3. A refrigerator as defined in claim 2 in which the operating means is responsive to the temperature of said evaporator portion nearest the entrance of said circulating air into said mixing compartment from the above freezing compartment.

4. A refrigerator including means enclosing a below freezing storage compartment and an above freezing storage compartment, means forming a mixing compartment separated from said compartments, an evaporator portion associated with said mixing compartment, means for circulating air from said below and above freezing compartments through said mixing compartment and returning the cooled air to said below and above freezing compartments in amounts sufiicient to maintain normally said compartments at desired below and above freezing temperatures, refrigerant liquefying means operatively connected to said evaporator portion, a double throw temperature responsive defrost control switch responsive to the temperature of said evaporator portion having a normally movable contact member and two normally stationary contacts alternately contacted by said movable contact member, electrical supply conductors, electrical means for defrosting said evaporator portion having an electrical connection with one of said normally stationary contacts and with one of said electrical supply conductors, electrical operating means for said liquefying means having an electrical connection with one of said supply conductors, said movable contact member having an electrical connection with one of said supply conductors, and first and second temperature responsive switches electrically connected between the other normally stationary contact and said electrically operating means responsive respectively to the temperature of the below and above freezing compartments for assuring adequate cooling of both compartments and for influencing the operation of the defrost control to defrost position when said evaporator portion is coated with frost.

5. A refrigerator as defined in claim 4 in which said temperature responsive defrost control switch is responsive to the temperature of said evaporator portion nearest the entrance of said circulating air into the mixing compartment from the above freezing compartment and exposed to the air flowing from said above freezing compartment.

References Cited by the Examiner UNITED STATES PATENTS 3,138,006 6/1964 Moorman 62156 MEYER PERLIN, Primary Examiner, 

1. A REFRIGERATOR INCLUDING MEANS ENCLOSING A BELOW FREEZING STORAGE COMPARTMENT AND AN ABOVE FREEZING STORAGE COMPARTMENT, MEANS FORMING A MIXING COMPARTMENT SEPARATED FROM SAID COMPARTMENTS, AN EVAPORATOR PORTION ASSOCIATED WITH SAID MIXING COMPARTMENT, MEANS FOR CIRCULATING AIR FROM SAID BELOW AND ABOVE FREEZING COMPARTMENTS THROUGH SAID MIXING COMPARTMENT AND RETURNING THE COOLED AIR TO SAID BELOW AND ABOVE FREEZING COMPARTMENTS IN AMOUNTS SUFFICIENT TO MAINTAIN NORMALLY SAID COMPARTMENTS AT DESIRED BELOW AND ABOVE FREEZING TEMPERATURES, REFRIGERANT LIQUEFYING MEANS OPERATIVELY CONNECTED TO SAID EVAPORATOR PORTION, A DEFROSTING SWITCH HAVING A SET OF NORMALLY CLOSED CONTACTS, ELECTRICAL OPERATING MEANS FOR SAID LIQUEFYING MEANS, A THERMOSTATIC CYCLING CONTROL SWITCH RESPONSIVE TO TEMPERATURES OF SAID BELOW FREEZING COMPARTMENT AND A SECOND TEMPERATURE RESPONSIVE SWITCH RESPONSIVE TO THE TEMPERATURE OF SAID ABOVE FREEZING COMPARTMENT, SAID CYCLING CONTROL SWITCH AND SAID SECOND 